/*
 * Copyright (C) 2009 Andrzej K. Haczewski <ahaczewski@gmail.com>
 *
 * DISCLAIMER: The implementation is Git-specific, it is subset of original
 * Pthreads API, without lots of other features that Git doesn't use.
 * Git also makes sure that the passed arguments are valid, so there's
 * no need for double-checking.
 */

#include "../../git-compat-util.h"
#include "pthread.h"

#include <errno.h>
#include <limits.h>

static unsigned __stdcall win32_start_routine(void *arg)
{
        pthread_t *thread = arg;
        thread->arg = thread->start_routine(thread->arg);
        return 0;
}

int pthread_create(pthread_t *thread, const void *unused,
                   void *(*start_routine)(void*), void *arg)
{
        thread->arg = arg;
        thread->start_routine = start_routine;
        thread->handle = (HANDLE)
                _beginthreadex(NULL, 0, win32_start_routine, thread, 0, NULL);

        if (!thread->handle)
                return errno;
        else
                return 0;
}

int win32_pthread_join(pthread_t *thread, void **value_ptr)
{
        DWORD result = WaitForSingleObject(thread->handle, INFINITE);
        switch (result) {
                case WAIT_OBJECT_0:
                        if (value_ptr)
                                *value_ptr = thread->arg;
                        return 0;
                case WAIT_ABANDONED:
                        return EINVAL;
                default:
                        return err_win_to_posix(GetLastError());
        }
}

int pthread_cond_init(pthread_cond_t *cond, const void *unused)
{
        cond->waiters = 0;
        cond->was_broadcast = 0;
        InitializeCriticalSection(&cond->waiters_lock);

        cond->sema = CreateSemaphore(NULL, 0, LONG_MAX, NULL);
        if (!cond->sema)
                die("CreateSemaphore() failed");

        cond->continue_broadcast = CreateEvent(NULL,    /* security */
                                FALSE,                  /* auto-reset */
                                FALSE,                  /* not signaled */
                                NULL);                  /* name */
        if (!cond->continue_broadcast)
                die("CreateEvent() failed");

        return 0;
}

int pthread_cond_destroy(pthread_cond_t *cond)
{
        CloseHandle(cond->sema);
        CloseHandle(cond->continue_broadcast);
        DeleteCriticalSection(&cond->waiters_lock);
        return 0;
}

int pthread_cond_wait(pthread_cond_t *cond, CRITICAL_SECTION *mutex)
{
        int last_waiter;

        EnterCriticalSection(&cond->waiters_lock);
        cond->waiters++;
        LeaveCriticalSection(&cond->waiters_lock);

        /*
         * Unlock external mutex and wait for signal.
         * NOTE: we've held mutex locked long enough to increment
         * waiters count above, so there's no problem with
         * leaving mutex unlocked before we wait on semaphore.
         */
        LeaveCriticalSection(mutex);

        /* let's wait - ignore return value */
        WaitForSingleObject(cond->sema, INFINITE);

        /*
         * Decrease waiters count. If we are the last waiter, then we must
         * notify the broadcasting thread that it can continue.
         * But if we continued due to cond_signal, we do not have to do that
         * because the signaling thread knows that only one waiter continued.
         */
        EnterCriticalSection(&cond->waiters_lock);
        cond->waiters--;
        last_waiter = cond->was_broadcast && cond->waiters == 0;
        LeaveCriticalSection(&cond->waiters_lock);

        if (last_waiter) {
                /*
                 * cond_broadcast was issued while mutex was held. This means
                 * that all other waiters have continued, but are contending
                 * for the mutex at the end of this function because the
                 * broadcasting thread did not leave cond_broadcast, yet.
                 * (This is so that it can be sure that each waiter has
                 * consumed exactly one slice of the semaphor.)
                 * The last waiter must tell the broadcasting thread that it
                 * can go on.
                 */
                SetEvent(cond->continue_broadcast);
                /*
                 * Now we go on to contend with all other waiters for
                 * the mutex. Auf in den Kampf!
                 */
        }
        /* lock external mutex again */
        EnterCriticalSection(mutex);

        return 0;
}

/*
 * IMPORTANT: This implementation requires that pthread_cond_signal
 * is called while the mutex is held that is used in the corresponding
 * pthread_cond_wait calls!
 */
int pthread_cond_signal(pthread_cond_t *cond)
{
        int have_waiters;

        EnterCriticalSection(&cond->waiters_lock);
        have_waiters = cond->waiters > 0;
        LeaveCriticalSection(&cond->waiters_lock);

        /*
         * Signal only when there are waiters
         */
        if (have_waiters)
                return ReleaseSemaphore(cond->sema, 1, NULL) ?
                        0 : err_win_to_posix(GetLastError());
        else
                return 0;
}

/*
 * DOUBLY IMPORTANT: This implementation requires that pthread_cond_broadcast
 * is called while the mutex is held that is used in the corresponding
 * pthread_cond_wait calls!
 */
int pthread_cond_broadcast(pthread_cond_t *cond)
{
        EnterCriticalSection(&cond->waiters_lock);

        if ((cond->was_broadcast = cond->waiters > 0)) {
                /* wake up all waiters */
                ReleaseSemaphore(cond->sema, cond->waiters, NULL);
                LeaveCriticalSection(&cond->waiters_lock);
                /*
                 * At this point all waiters continue. Each one takes its
                 * slice of the semaphor. Now it's our turn to wait: Since
                 * the external mutex is held, no thread can leave cond_wait,
                 * yet. For this reason, we can be sure that no thread gets
                 * a chance to eat *more* than one slice. OTOH, it means
                 * that the last waiter must send us a wake-up.
                 */
                WaitForSingleObject(cond->continue_broadcast, INFINITE);
                /*
                 * Since the external mutex is held, no thread can enter
                 * cond_wait, and, hence, it is safe to reset this flag
                 * without cond->waiters_lock held.
                 */
                cond->was_broadcast = 0;
        } else {
                LeaveCriticalSection(&cond->waiters_lock);
        }
        return 0;
}